At the UKs Sheffield University (SU) a team led by Professor Will Zimmerman in the Department of Chemical and Process Engineering believes they have developed an inexpensive way of producing microbubbles that can float algae particles to the surface of the water, making harvesting easier, and saving biofuel-producing companies time and money.
One of the cost of production problems that holds algae back as a major biomatter resource is an efficient cost-effective method of harvesting and removing the water from the algae for it to be processed.
Algae have the potential to be a very efficient biofuel producer. The one cell plant produces oil that can be processed to create a useful biofuel. Biofuels made from plant material are considered important alternatives to fossil fuels. The carbohydrate portion can be used for food or to make more fuel.
The SU team’s new technique builds on previous research in which microbubbles were used to improve the way algae is cultivated. The early work used the microbubble technology to improve algae production methods, allowing producers to grow crops more rapidly and more densely and earned Zimmerman and the team the Moulton Medal, from the Institute of Chemical Engineers. The research paper is published in Biotechnology and Bioengineering.
Professor Zimmerman outlines the story saying, “We thought we had solved the major barrier to biofuel companies processing algae to use as fuel when we used microbubbles to grow the algae more densely. It turned out, however, that algae biofuels still couldn’t be produced economically, because of the difficulty in harvesting and dewatering the algae. We had to develop a solution to this problem and once again, microbubbles provided a solution.”
Microbubble Algae Separation at the University of Sheffield.
Microbubbles have been used for flotation before: water purification companies use the process to float out impurities, but it hasn’t been done in this context, partly because the previous methods have been very expensive.
The new system developed by Zimmerman´s team uses as little as one tenth of a percent of the energy to produce the microbubbles. Additionally, the cost of installing the Sheffield microbubble system is predicted to be much less than existing flotation systems.
Zimmerman explains the technology saying, “What we’ve found is that we can separate the microalgae from the water or harvest it using microbubbles that are created by a fluidic oscillator. A fluidic oscillator switches flows rapidly from one outlet to another, using feedback to do so with no moving parts. It is like an opening and closing mechanical valve that results in pulsing flow. Our bubbles are made under laminar flow and we use practically no more energy than is required to make the interface of the bubble.”
As a result of the low energy input, the bubbles rise very slowly, which is crucial as it means the algae particles can attach themselves to the bubbles more easily. Two chemicals added to the liquid in the process, a flocculant and a coagulant to help the algae bond to the rising microbubbles.
“The idea is to create a surface on the algae particles that is hydrophobic so the microbubbles are attracted to it,” said Zimmerman. When the bubbles and the particles reach the surface, the flocculant and the coaggulant keep the algae in a fixed layer. The blanket of algae can then be skimmed off the surface with something such as a belt skimmer. “In the lab, we use a knife.”
Zimmerman explained that the process is much cheaper than attempting to make microbubbles through an industrial process known as dissolved air flotation, which generates bubbles that are too turbulent to harvest algae.
Next up for the technology is to develop a pilot plant to test the system at an industrial scale. Professor Zimmerman is already working with Tata Steel at their site in Scunthorpe, where Tata Steel is recovering and using CO2 from their flue-gas stacks. Zimmerman and Tata plan to continue the partnership to test the new system.
The SU team’s technology may have other soon to be used attributes. Lakes that have a build-up of nutrients causing algal blooms to form called eutrophication, often attributed to agricultural fertilizers entering water bodies, need the algae harvested and removed instead of left to die and decompose.
The SU team is already in talks with Ken Shu, a scientific adviser to the Chinese government, to set up pilot-scale trials on remediating algal blooms in eutrophied lakes in China.
Zimmerman explains, “China has demographic drinking-water problems. They’re running out because the lakes that used to be used for drinking water are all eutrophied with algal blooms.”
It looks good in the lab. A lot of ideas have come and gone in trying to capture the algae cells in a low cost harvest. Algae, naturally, are pretty good at keeping themselves separate with each basking in the sunlight. It’s a significant attribute that makes the very high productivity possible as well as makes the harvest problematic.
Let’s hope the Brits have it nailed down now.
By. Brian Westenhaus